Foam Roofing Cost Comparison

Question:How much does a foam roof cost?Short Answer:About the same as a Tar & Gravel or BUR Roof

Flat Roofing Material Cost Comparison

Generally, a polyurethane foam roof costs about the same as a Built Up Roof (BUR) with underlying insulation. However, a polyurethane foam roof is unique because it is the only roof type that can both insulate and protect against leaks as a single monolithic barrier.

Most contractors will not recommend a BUR roof is installed with underlying insulation, since the roof membrane is usually stretched towards the edges of the roof where there is no insulation. This causes stretching of the membrane since the roof tends to heat or cool faster in these areas, causing both excessive contraction and expansion of the roof membrane. This is in sharp contrast to the rest of the roof membrane, which will not shrink or stretch as much, due to underlying insulation. This tug of war causes wear and tear on the roof membrane, especially near the edge of a roof. In the case of a BUR roof, without reflective coatings, the surface temperature can exceed 150 degrees Fahrenheit on a summer day. ‘Cooking’ a roof membrane like this can cause it to tear and crack prematurely. And once a roof membrane is compromised, water can seep in and quickly cause large areas of a roof to deteriorate. Just a few months of water penetration can cause major deterioration of a roof membrane.

Image: A three dimensional cut-away of a BUR roof (Built Up Roof).

Some Flat Roofing Materials

There are a plethora of flat roofing materials, however, not all are of equal quality. An EPDM (rubber roof) or a singly ply roof, sealed either by tars or adhesives are lower quality than a typical bur roof. This is because they generally last less than 5-10 years, while a higher quality BUR roof may last more than 10 years. Generally, a BUR roof consists of a few semi flexible membrane layers, water-proofed with water resistant modified bitumen.

Keep in mind, coal tars, which are mostly no longer in use, are a known carcinogenic substance (not as severe as asbestos–otherwise, this would be more widely known). Modified bitumen comes from oils, refined at much lower temperatures than coal tar, and is a much safer substance. Recently, the sharp rise in the cost of a barrel of oil has been passed on to the roofing industry. As the costs of asphalt continue to increase, and the cost of a high quality polyurethane foam roof remains more steady, SPF or foam roofing continues to become more affordable.

Image: A three dimensional cut-away of a PVC plastic roof (polyvinyl chloride based highly flexible plastic membranes). Picture from www.jmeagle.com

Cost Comparison

Cost of course varies by many factors, including geographic location, and size and type of job. While prices may be quoted anywhere between $3-$12 per square foot, these are often effected by several factors. The quality of the materials being used, the labor costs to install these materials, and any associated warranty, contractor insurance, or bonding costs which get passed on to the customer.

Up-Front Cost Factors:

Roof Size: for example, large projects are often cheaper per square foot due to installation efficiencies gained with economies of scale.

Roof Penetrations and obstructions: if your roof is a minefield of obstructions full of skylights, pipes, and AC equipment, you can expect higher installation costs due to increased labor requirements.

Materials Used: EPDM and Single ply roofs are cheaper materials that will not last as long. Higher quality roofing such as polyurethane foam may cost a bit more, but it will insulate and last the life of the building. In contrast, a roof, such as Tar & Gravel, with insulation will cost about the same as an SPF roof.

Location: Is your property in Beverly Hills or next door to the Beverly Hillbillies? Expect higher costs with higher real estate expenses, since your local contractor will need to pay rent to be located within range of your home.

Condition of Existing Substrate & Roof: Can the existing roof membrane be re-used, or must it be torn off? Are there layers of asbestos or other harmful substances under your roof membrane? Do you have dry-rot or other failing structures. Do drains, vents, skylights or other roof penetrations need to be replaced?

Do you need to install solar power or replace vents drains etc? It is much more cost effective to do all of this at once. Imagine if your solar power installers caused a leak in your roof, and neither contractor (roofing or solar) wanted to fix the issue because each blamed the other. There are some contractors like Dura-Foam Solar Center (California, Bay Area) which can do both roofing and solar installations, saving you a potential headache in the long run.

Re-Roof Before Making Other Improvements

Re-roofing is often an expensive, but important part of home maintenance which cannot be avoided. If you’re thinking of remodeling a home, you should probably update your roof first. The roof will protect your interior carpet, paint, furniture and other belongings. One way to save money, is to extend the life of the roof you already have.

Simply getting on your roof and making sure no drains are clogged by leaves, dirt, rocks or other obstructions can go a long way in persevering the life of your roof. At a minimum, this should be done every 6 months on a flat roof or more often if you’re home is surrounded by a lot of trees (people in places like Palo Alto, which have more trees than people are more at risk). If a drain is left clogged, and large quantities of standing water form, it can quickly destroyed a BUR, EPDM, Single Ply or Tar & Gravel roof. Although we do not usually think of water as a solvent, it is truly a powerful one, especially over long periods of time. A simple clogged rain can devastate a roof over the course of a year if standing water is left on a roof for an extended period of time (a few months or a year).

Long Term Costs

When installing a roof, it is good to consider the long term cost impact. If you have a warehouse or an Eichler with no space or provisions for insulation (except for the roof), adding an insulated roof can pay big dividends in the long run. Also consider the importance of cool roof coatings; simply changing the color of a roof to something reflective could cut down summer cooling bills by 30% or more. Medium Density Sprayed Polyurethane Foam Roofing conforms to a roof and generally has an R-Value around 6 to 8 per inch of material thickness. That means, one inch of foam is as effective as 6 to 8 inches of solid wood.

In practice due to factors such as vapor trapping (foam forms a barrier), and due to the density of foam (it is light, but heavier than air–of course), foam can often be 4 times more effective than fiberglass. Those of us who have lived in older, poorly insulated homes know that heating and cooling bills can really get out of control with a poorly insulated home. This is just one final cost factor which should be considered when comparing an insulated roof (like foam roofing) with other roofing materials (like EPDM, Single Ply, or BUR with no insulation).

Summary

Giving the cost of a foam roof in general is too difficult due to large cost differences based on location, size of job, and other factors. The best rule of thumb we can give is that a foam roof costs about the same as a BUR (or tar and gravel) roof, especially if the roof is installed with insulation. If you are in the California Bay Area (near San Francisco or San Jose), and you are interested in learning the cost of a foam roof, click here for a Free Estimate on a new foam roof.

The foam roof should be cheaper since it takes little labor. The roof can be done in 2 days by 2 persons. The materials cost is about $3,thus the profit is very large. Such roof should not cost more than $10,000 for 2,000 sq ft house.

For 1,500 square foot roof area the cost should not be higher than $10,000. Materials are cheap and this is a spraying job. Overall less labor and material costs than for any other roof like tar and gravel or membrane.

The US costs are shown starting at $2.50 per square foot. Probably in Alabama. In the Bay Area it should be about $5 per square foot. Contractors artificially increase the price to match the pricing of labor intensive roofs. E.g. not what our cost plus profit but what the market can bear.

Ben: There’s no artificial increase. This is economics 101; in the Wealth of Nations, Adam Smith tells us that in a free market economy (which is what the USA is, for all practical purposes) price is determined by “rent of land”, “cost of [employee] wages” and “profit of stock” (compensates the capitalist for risking his resources). The Bay Area is also a free market economy, so the price you see matches the cost.

Scott: that’s too big of a generalization. Square foot is only one factor in the cost of a roof. Does the roof need to be torn off? Are there many pipes, and skylights or other roof penetrations? Is this just a 1 story building or is a 4 story building where additional precautions (costs) must be taken to keep the workers safe? Also, tar & gravel & membrane are very cheap materials. Foam roofing is a more expensive, more durable, higher quality material. I’ve never seen a membrane or tar and gravel roof last 30+ years. However, it’s not uncommon for a foam roof to last 30+ years. Additionaly, how much foam is being applied to the roof? 1″? 1.5″? 2″? This will also effect the cost. Finally, the quality of the coating (e.g. thickness, fire rating, & other factors) will effect the cost too.

I would like to know how a foam roof fares during fire? Is it easily flammable? I want to apply this type of roof to a home that is surrounded by an area where grass fires can occur, and the roof could be subject to burning embers during a fire. How does it compare to behavior of a roof that is a shake roof, a roof with fiberglass shingles, and of course a BUF of membrane, tar and gravel. Thanks!

Yes, laying wood planks directly over the roof surface is possible. However, you may find dirt to collect over time and result in obstructed drainage. Integrating stainless steel supports for a slightly elevated deck structure is one of the best long-term solutions I’ve seen.